It seems I got the famous problem with the lcd. The letters wont appear.Its a 16x2 blue lcd.

Have checked the cables over and over again and I find it correct.The LCD starts and the backlight shows, but not the letters. Sometimes the white boxes flashes a millisec or so, then disappears.

Im followed the Hello world guide wich comes with the arduino. I got the 10K potentiometer. And I have tried with and without it, same result.I also cant change the contrast with the potentiometer coupled on. Ive checked the outputvoltage on it,and it works! Anybody that got an idea? Can link a video if someone want a look.

The LCD starts and the backlight shows, but not the letters.Sometimes the white boxes flashes a millisec or so, then disappears.

Are you using a current limiting resistor with your backlight?

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I got the 10K potentiometer. And I have tried with and without it, same result.I also cant change the contrast with the potentiometer coupled on.

You must use the potentiometer and you must get the contrast working before you proceed any further. If you can't get a row of boxes to appear then you are wasting your time trying to display any text.

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Ive checked the outputvoltage on it,and it works!

Explain what voltage(s) you measured and why you think it works. When it really works you will be able to see a row of boxes on the screen.

When I checked the potentiometer,I used a voltmeter and looked at the output voltage when the arduino was running and only coupled in the voltage from the arduino.I think the potentiometer works because it gives diffrent voltage to the LCD. It also changes the contrast a liiiiiitle liiiitle bit.Little bit hard to see it in the video tho.Here is the video: https://vimeo.com/54703995

Here is a clearly pic of how I wired everything, and a pic I got from the manual to compare with.http://tinypic.com/view.php?pic=2ldubtt&s=6

Here is a video showing how the white boxes flashes when I turned the potentiometer with everything wired:https://vimeo.com/54704282

Here is the manual for the LCD from the manufactor:http://www.kjell.com/.mvc/Document/File?id=b6e33422-63ff-48be-b140-a04a0114d7ef

And here is the code I was runnning with everyting coupled in the pic:

I think the potentiometer works because it gives diffrent voltage to the LCD. It also changes the contrast a liiiiiitle liiiitle bit.

You should be able to vary the voltage at pin 3 from 0 to 5 Volts (with respect to pin 1). The display should be blank at +5 Volts and you should have a single solid row of blocks at 0 Volts. The proper setting, which will still show the blocks, will be around 0.4 Volts for your LCD.

Look in the lower left box in the 'Description of Terminals' and you will see that the backlight must be supplied with no more than 4.5 Volts.

This means that you must use a series resistor to drop the voltage and at the same time limit the current through tbe LED backlight.

Don

I've recently tested to connect the backlight to the 3v pin on the arduino instead. But its the same. (Ive solder the wires on the backside of the LCD)Could I have destoyed the backlight when I wired it to the +5V?

Nowhere in there does it ever mention needing to solder the connectionsto the LCD module. It shows them soldered in the photo, but it never says it in the text/instructions.In fact it doesn't even list solder in the h/w requirements.Ignoring the obvious typo of "LED" vs "LCD" this is really the only instructions:

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To wire your LED screen to your Arduino, connect the following pins

And then a fritzing diagram below.

So the issue is that users can follow the tutorial to the letter and have everything"wired" correctly and end up with a non working or even semi working LCD because the tutorial failsto mention the requirement of soldering the connections to the LCD.

Unfortunately trying to get the Arduino team to change anything is worsethan pulling teeth. But clearly this needs to get updated.

I've recently tested to connect the backlight to the 3v pin on the arduino instead.

Regardless of how you power an LED you still need some way to limit the current and this almost always involves the use of a resistor.

Depending upon the LED configuration in the backlight circuit the 3 V supply may not provide enough voltage and/or current to work properly.

You should power the backlight from a 5 Volt supply using a resistor in between the supply and one of the backlight pins. Unfortunately your data sheet does not supply enough information to determine the required resistance so you will have to experiment. I would start out with about 150 ohms and see if the voltage across the LED is then within specifications and if the backlight is sufficiently bright.

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Could I have destoyed the backlight when I wired it to the +5V?

You didn't help it or the Arduino power supply at all, but you probably didn't destroy either of them (yet) either.

Unfortunately trying to get the Arduino team to change anything is worse than pulling teeth. But clearly this needs to get updated.

That is the understatement of the year.

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It appears that github is now being used for issues but I wen't ahead and put it on the google code page as well.

This doesn't help the fact that most beginners rely on the 'official' Arduino pages as gospel truth and mere mortals cannot correct those pages even when they are blatantly incorrect, incomplete, or obsolete.